In general, noise introduced into a vehicle may be classified into a noise generated at an engine and introduced through a vehicle body and a noise generated when tires are contacted with a road surface and introduced through a vehicle body. There may be two ways to block theses noises such as improving sound-absorbing performance and improving noise insulation performance. Sound-absorbing means that generated sound energy is converted into thermal energy and then dissipated while it is transmitted through internal route of a material, and noise insulation means that generated sound energy is reflected and blocked by a shelter.
According to such characteristics of sound, in order to improve Noise, Vibration & Harshness (NVH) of a vehicle in general, a heavier and thicker sound-absorbing material has been mainly used in luxury cars. However, when such sound-absorbing material is used, noise may be reduced, but there is a problem of deteriorating fuel efficiency by increasing vehicle weight.
Further, in order to overcome problems of the conventional sound-absorbing material, a method in which porosity of the material is improved by thinning fiber thickness have been developed thereby improving sound-absorbing performance and also reducing weight of fiber aggregate. However, this method may also have a weakness such that needs surface density of the fiber aggregate may be improved in order to improve the desired NVH performance.
Further, in order to manufacture non-woven type fiber aggregate, staple fiber and binder fiber are mixed together at a proper ratio. As the binder fiber, in general, staple fiber manufactured by conjugate-spinning regular polyester is used for an inner layer and low melting polyester is used for an outer layer.
However, when using this conventional binder fiber with the low melting polyester, the fiber aggregate is hardened, and thus there may be a problem that vibration generated by sound wave propagation and transmitted to matrix structure is not fully attenuated, thereby reducing sound absorbtion coefficient mainly at low frequency region.
The matters described as the related art have been provided only for assisting in the understanding for the background of the present invention and should not be considered as corresponding to the related art known to those skilled in the art.